MICROMACHINED SUBMINIATURE CONDENSER MICROPHONES IN SILICON

Silicon subminiature microphones can be manufactured with the methods of micromachining technology. Several condenser type microphones have been designed and fabricated at our institute. Capacitive microphones are described, which have a structured back electrode and a membrane of silicon nitride. A smooth frequency response up to 30 kHz with a maximum open-circuit sensitivity of 10 mV/Pa is obtained. A special design of a capacitive sensor has been realized with the FET microphone. The drain current of a field-effect transistor with a suspended gate is modulated by the vibrations of the membrane. This design represents the first suspended-gate sensor, the drain current of which is deflection controlled. Design, construction and experimental results of sensitivity and frequency response are given.